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Cabbage, Cauliflower, Turnips, Cucumbers, Melons, and Related Crops

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Cabbage, Cauliflower, Turnips, Cucumbers, Melons, and Related Crops Market Diseases of Cabbage, Cauliflower, Turnips, Cucumbers, Melons, and Related Crops «• S. OEPT. Of AGíHCütn«E| UPRARV 0CT12I96Î ^wnm spRMi Kectms Glen B. Ramsey and M. A. Smith Agriculture Handbook No. 184 UNITED STATES DEPARTMENT OF AGRICULTURE Agricultural Marketing Service Market Quality Research Division THIS REPORT is one of a group of publications on market diseases of fruits and vegetables. The publications are designed to aid in the recognition and identification of pathological conditions of economic importance affecting fruits and vegetables in the channels of marketing in order to facilitate inspection of these food products and to prevent losses from such conditions. Other reports on market diseases of fruits and vegetables issued by the U.S. Department of Agriculture include : Miscellaneous Publications 98. Potatoes. Revised Jan. 1949. 168. Apples, Pears, Quinces. Revised Nov. 1951. 228. Peaches, Plums, Cherries, and Other Stone Fruits. Re- vised Feb. 1950. 340. Grapes and Other Small Fruits. July 1939. 440. Asparagus, Onions, Beans, Peas, Carrots, Celery, and Re- lated Vegetables. Sept. 1941. 498. Citrus and Other Subtropical Fruits. June 1943. Agriculture Handbooks 28. Market Diseases of Tomatoes, Peppers, and Eggplants. June 1952. 155. Market Diseases of Beets, Chicory, Endive, Escarole, Globe Artichokes, Lettuce, Rhubarb, Spinach, and Sweet- potatoes. April 1959. Miscellaneous Publications 228, 340, and 440 are out of print but may be consulted in libraries. This publication supersedes Miscellaneous Publication 292, "Market Diseases of Fruits and Vegetables; Crucifers and Cucurbits." Market Diseases t Cabbage, Cauliflower, Turnips, Cucumbers, Melons, and Related Crops Agriculture Handbook No. 184 ► UNITED STATES DEPARTMENT OF AGRICULTURE Agricultural Marketing Service Market Quality Research Division September 1961 For sale by the Superintendent of Documents, U.S. Government Printing OflSce Washington 25, D.C. CONTENTS Page Page Crueifers 1 Cucumber 21 Cabbage 1 Anthracnose 22 Alternaría leaf spot 2 Bacterial spot (angular leaf Bacterial soft rot 3 spot) 23 Black rot 23 Bacterial zonate spot 4 Cottony leak 24 Black leaf speck 4 Low temperature break- Black rot 5 down 24 Downy mildew 6 Mosaic 25 Freezing injury 7 Scab 25 Gray mold rot 8 Soil rot 25 Mosaic 9 Muskmelon 26 Rhizoctonia head and root Alternarla rot 26 rots 9 Anthracnose 27 Rhizopus soft rot 10 Bacterial soft rot 28 Bacterial spot 29 Sunscald 11 Blue mold rot 29 Thrips (Edema) 11 Charcoal rot 30 Tipburn 11 Cladosporium rot 30 Watery soft rot _ 12 Diplodia rot 31 Chinese cabbage 13 Fusarium rot 32 Brussels sprouts 13 Low temperature breakdown. 33 Broccoli 14 Phytophthora rot 33 Cauliflower 14 Pink mold rot 34 Bacterial leaf spot 14 Rhizopus soft rot 35 Boron deficiency 15 Pumpkins 36 Brown rot 16 Squash 36 Ring spot 16 Alternarla rot 36 Black rot (gummy stem Collards and kale 17 blight) "_ 37 Cress 17 Blossom end rot 37 Horseradish 17 Watermelon 38 Bacterial root rots 18 Anthracnose 38 Pénicillium root rot 18 Black rot 39 Rhizoctonia root rot 18 Blossom end rot 40 Kohlrabi 18 Bruising (mechanical injury) 40 Mustard 19 Charcoal rot 40 Radish 19 Fusarium rot 41 Black spot 19 Internal rind spot 41 White rust 19 Phytophthora rot 41 Watermelon pimples 42 Rutabaga and turnip 20 Pythium rot 42 Alternarla root rot and leaf Sclerotium rot 43 spot 20 Soilrot 43 Anthracnose 20 Speckle 43 Clubroot 21 Stem end rot 44 Cucurbits 21 Literature cited 45 ii Market Diseases of CABBAGE, CAULIFLOWER, TURNIPS, CUCUMBERS, MELONS, AND RELATED CROPS By GLEN B. RAMSEY, principal pathologist,^ and M. A. SMITH, senior patholo- gist, Market Quality Research Division, Agricultural Marketing Service CRUCIFERS The various members of the crucifer group supposedly are horti- cultural varieties which have been developed by cultivation from the wild Brassica olerácea. Thus the headless types (kale and coUard, etc.) "are B. olerácea var. viridis L.; the budding type (brussels sprouts), var. gemmifera DC; the floral head types (cauliflower and flowering broccoli), var. hotrytis L. and var. itálica Plenck; the en- larged stem type (kohlrabi), var. caulo-rapa L.; and the leafy head type (cabbage), var. capitata L. CABBAGE Cabbage is used for food as salad and as a cooked vegetable, and a considerable amount is fermented and eaten as sauerkraut. Cab- bage, like most other cultivated crucifers, belongs to the genus Brassica. The marketability of cabbage for table purposes is affected by many factors, the foremost being crispness, solidity of head, color, and freedom from blemishes and decay. Since field diseases often affect the crispness, solidity, and color of cabbage, they are both a direct and an indirect factor in its marketability. Lack of crispness may be due to poor growing conditions, to field diseases, to excessive drying out in storage, or to the respiratory activities of the tissues. Excessive loss of crispness because of res- piration may result from too high a temperature during transit and storage or from too long a transit or storage period. Several diseases which seriously affect production may also directly affect the marketability of the heads. Foremost among these is black rot {XantKonwnas camfestris (Pam.) Dows.). Others are alternarla leaf spot {Alternaría hrassicae (Berk.) Sacc. and A. olerácea Mil- brath), bacterial leaf spot {Pseudomonas iimculicola (McCull.) F. L. Stevens), downy mildew {Peronospora parasítica (Fr.)), and Rhizoctonia head rot {PelliculaHa filavientosa (Pat.) Kogers). iNow retired. There are several diseases which only occasionally cause losses in the field, but Avhich are exceedingly important in the later stages of distribution and in storage. These are bacterial soft rot (Enmnia carotovora), gray mold rot {Botrytis cinérea (Pers.)), rhizopus soft rot {Rhizojma stolonifer (Fr.)), and watery soft rot {Sclerotinia sclerotiorum (Lib.) DBy). Often these also cause heavy indirect losses in transit and storage by necessitating heavy trimming. (See 10, 11, 26, 27, k6, 6k, 68, 89, 101, lOl^.y ALTERNARíA LEAF SPOT A\\Qtnat\a spp. Occurrence and Importance Alternaría leaf spot is a widelj' distributed disease that occurs on cabbage, cauliflower, broccoli, and most other plants belonging to the mustard family. In wet seasons this leaf spot has been known to reduce the yield of cabbage by more than 50 percent. The market losses are due to decay which develops in transit and storage, to secondaiy decay for wliich it opens the way, and to blemishes which render the heads unsightly and necessitate heavy trimming. Symptoms The first symptom of alternaría leaf spot is the appearance of small grayish-brown to black spots about i/^e inch in diameter (pi. 3, F). They may appear at any time during the life of the cabbage plant. They usually are most conspicuous on the outer, older leaA^es. The color of the spots depends somewhat on the color of the part of the leaf aiïected. Old spots may range up to 1 inch or more in diameter. Sometimes the spots produced by A. hrassica-e are marked by light- and dark-brown concentric zones that produce a "target board" appearance. A growth of dark brown to black mold is often present in a humid atmosphere (pi. 1, B). The spots caused by A. olerácea are not zonate and usually are not covered by a moldy growth until the leaves turn yellow or are shed. Bacterial soft rot and other secondary decay sometimes follow in these lesions. Causal Factors Three species of Alternaría have been reported as causing leaf spot of plants belonging to the mustard family. A. hra,ssicae is generally thought to be the cause of most losses, although A. olerácea also causes serious damage in some regions. Under moist conditions the spores of these organisms may germinate and cause infection within 24 hours. The spores germinate best between 63 and 70° F. Wounds are not necessary for infection. Although most infections are promi- nent on the wrapper and older head leaves, the age of the plant ap- parently has little to do with the infection. High humidity and moderate temperatures favor the spread and development of this disease. Low temperatures (35^5° F.) and low humidity greatly inhibit infection and decay. Control Measures Severely spotted heads of cabbage and other plants of this family should be closely trimmed before shipment. Shipments to distant ' Italic numbers in parentlieses refer to items in the Literature Cited, p. 45. 2 markets should be refrigerated to 40-45° F. during transit. Cabbage to be held in storage for any great length of time should be kept at 35° F. or slightly below. {See 89,93.) BACTERIAL SOFT ROT Erwinia carotovora (Jones) Holland and other bacteria Occurrence and importance Bacterial soft rot of cabbage and other members of the mustard family often causes serious losses during marketing. This is be- cause bruised and wounded tissues are readily atfected, and the causal organism is a secondary invader of tissues killed or weakened by most of the parasitic and some nonparasitic diseases. It often fol- lows black rot, clubroot, downy mildew, or alternarla leaf spot, and causes most of the damage following freezing. Ordinarily, soft rot is of little importance in the field except as a secondary invader following other diseases. At times dead and dying heads in the field develop soft rot and in cutting the crop for marketing the knives become contaminated, thus leading to infection of subsequent heads. Such heads show stump or butt rot by the time they reach the market (pi. 3, C). Symptoms On cabbage and brussels sprouts the first symptoms usually show as watersoaked or greasy spots on the leaves as biiiises or as white to grayish, soft areas at tlie base of the heads. Small lesions have no appreciable odor but extensive decay has a very putrid odor. INHien this disease follows black rot and other diseases frequently a large proportion of the head is converted into a brownish-black slimy mass.
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